Well, I've worked remotely for 16 years and in most meetings I don't get
to see the slides until the meeting starts. Usually I can only see them
via some conferencing tool. Sometimes I get a copy in mail the week
after. So I think the IETF is already doing pretty well at making
materials available, and insisting on getting slides far in advance of
the meeting is beyond what most people get in reality outside of the
IETF. I would call this a SHOULD not a MUST.